DESCRIPTION (Adapted from the application): Alzheimer's disease (AD) patients display a wide range of brain abnormalities. One of the hallmarks of AD is the florid deposition of senile plaques composed chiefly of A-beta. In some individuals familial early-onset AD (FAD) is attributable to specific mutations in the Amyloid Precursor Protein (APP) gene. Recently, it has been shown that A-beta levels are also affected by mutations in the Presenilin 1 and 2 genes (PS 1 and PS2). This argues strongly that AD may involve disturbances in APP metabolism. Correspondingly, there is tremendous interest in understanding the molecular actions of genes and agents that regulate Abeta production. Toward this goal much progress has been made. However, much remains to be elucidated regarding the subcellular mechanisms by which A-beta production is modulated, particularly in neurons (the cells most affected by AD). Post- translational processing of APP is highly complex, involving multiple pathways that function in cell-type specific ways. One of the primary goals of this project is to dissect and analyze the subcellular pathways that process APP and A-beta in neurons harboring mutations in PS 1. 1. To accomplish this, APP processing will be examined in primary neurons derived from transgenic mice with the PS 1 M 146V mutation "knocked into" the endogenous murine PS 1 gene. These cells will be infected with vectors (Semliki Forest virus and Herpes Simplex Virus-1/amplicons) engineered to express wild-type and FAD-related mutations in APP and PS 1, as well as APP trafficking/sorting mutations. Similarly, neurons from PS 1-deficient mice will be examined to further assess the role of PS 1 in APP processing. Interestingly estrogen, a substance with a number of neurobiological activities, has been shown to reduce A-beta production. To gain insight into the mechanisms by which estrogen opposes the generation of A-beta, another goal of this project is to identify the APP/A-beta processing pathways that are affected by the action of estrogen. These studies will be carried out in cultured primary rat neurons and the human neuronal NT2N cell line. These studies will likely provide new insights into the specific subcellular organelles and trafficking pathways that modulate neuronal APP and A-beta processing. This information may prove important in designing new strategies to prevent or control the pathological events underlying Alzheimer's disease.